This invention relates in general to transparent materials and more particularly to a transparent composite material containing glass fibers and a polymeric matrix and to a process for producing such a material.
Of all the materials that are transparent in the sense that they transmit radiant energy within the visible spectrum, glass is perhaps the most common, and well it should be, because it is hard and generally resistant to abrasion, chemically inert in the presence of most other substances, and relatively inexpensive. While these characteristics render glass quite suitable for use as a glazing material in buildings, glass is not totally acceptable for use as windows in transportation vehicles, particularly aircraft. This resides in the fact that glass is heavy, brittle to the extent that it may shatter upon impact, and difficult to form into complex shapes. Manufacturers of aircraft have accordingly to a large measure turned to transparent polymers, such as acrylic and polycarbonate, for the windows and canopies of their aircraft. But polymers, while being light in weight and certainly more flexible and easier to form than glass, do not possess the strength of glass.
As a consequence, the polymeric side windows of aircraft are of very limited area. Windshields and canopies possess far greater area, but they are usually thicker and thus heavier than side windows. Even so, windshields and canopies are more vulnerable, because they are subject to bird impacts.
A need exists in the aircraft industry for a lightweight transparent material that possesses substantial strength--indeed enough strength to withstand bird impacts. Yet the material should be thin and somewhat resilient so that it will flex without shattering when subjected to an impact concentrated in a small area. Moreover, the material should be relatively inexpensive. It should also be capable of being formed into the complex configurations typical of the canopies of fighter aircraft.